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3C454.3 Revelas the Structure and Physics of its 'Blazar Zone'

Description: Recent multi-wavelength observations of 3C454.3, in particular during its giant outburst in 2005, put severe constraints on the location of the 'blazar zone', its dissipative nature, and high energy radiation mechanisms. As the optical, X-ray, and millimeter light-curves indicate, significant fraction of the jet energy must be released in the vicinity of the millimeter-photosphere, i.e. at distances where, due to the lateral expansion, the jet becomes transparent at millimeter wavelengths. We conclude that this region is located at {approx} 10 parsecs, the distance coinciding with the location of the hot dust region. This location is consistent with the high amplitude variations observed on {approx} 10 day time scale, provided the Lorentz factor of a jet is {Gamma}{sub j} {approx} 20. We argue that dissipation is driven by reconfinement shock and demonstrate that X-rays and {gamma}-rays are likely to be produced via inverse Compton scattering of near/mid IR photons emitted by the hot dust. We also infer that the largest gamma-to-synchrotron luminosity ratio ever recorded in this object - having taken place during its lowest luminosity states - can be simply due to weaker magnetic fields carried by a less powerful jet.
Date: November 28, 2007
Creator: Sikora, M.; Moderski, R. & Madejski, G.M.
Partner: UNT Libraries Government Documents Department

Radio Loudness of AGNs: Host Galaxy Morphology and the Spin Paradigm

Description: We investigate how the total radio luminosity of AGN-powered radio sources depends on their accretion luminosity and the central black hole mass. We find that AGNs form two distinct and well separated sequences on the radio-loudness -- Eddington-ratio plane. We argue that these sequences mark the real upper bounds of radio-loudness of two distinct populations of AGNs: those hosted respectively by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the jet production efficiency in active galactic nuclei, and that this parameter is related to properties of the host galaxy. The revealed host-related radio dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars hosted by elliptical galaxies is radio quiet. We argue that the huge difference between the radio-loudness reachable by AGNs in disc and elliptical galaxies can be explained by the scenario according to which the spin of a black hole determines the outflows power, and central black holes can reach large spins only in early type galaxies (following major mergers), and not (in a statistical sense) in spiral galaxies.
Date: October 15, 2007
Creator: Stawarz, L.; Sikora, M. & Lasota, J.-P.
Partner: UNT Libraries Government Documents Department

Multiwavelength Observations of the Powerful Gamma-ray Quasar PKS 1510-089: Clues on the Jet Composition

Description: We present the results from a multiwavelength campaign conducted in August 2006 of the powerful {gamma}-ray quasar PKS 1510--089 (z = 0.361). This campaign commenced with a deep Suzaku observation lasting three days for a total exposure time of 120 ks, and continued with Swift monitoring over 18 days. Besides Swift observations, which sampled the optical/UV flux in all 6 UVOT filters as well as the X-ray spectrum in the 0.3--10 keV energy range, the campaign included ground-based optical and radio data, and yielded a quasi-simultaneous broad-band spectral energy distribution from 109 Hz to 1019 Hz. Thanks to its low instrumental background, the Suzaku observation provided a high S/N X-ray spectrum, which is well represented by an extremely hard power-law with photon index {Gamma}{approx_equal}1.2, augmented by a soft component apparent below 1 keV, which is well described by a black-body model with temperature kT {approx_equal}0.2 keV. Monitoring by Suzaku revealed temporal variability which is different between the low and high energy bands, again suggesting the presence of a second, variable component in addition to the primary power-law emission. We model the broadband spectrum of PKS 1510--089 assuming that the high energy spectral component results from Comptonization of infrared radiation produced by hot dust located in the surrounding molecular torus. In the adopted internal shock scenario, the derived model parameters imply that the power of the jet is dominated by protons but with a number of electrons/positrons exceeding a number of protons by a factor {approx} 10. We also find that inhomogeneities responsible for the shock formation, prior to the collision may produce bulk-Compton radiation which can explain the observed soft X-ray excess and possible excess at {approx} 18 keV. We note, however, that the bulk-Compton interpretation is not unique, and the observed soft excess could arise as well via some ...
Date: September 28, 2007
Creator: Kataoka, J.; Madejski, G.; Sikora, M.; Roming, P.; Chester, M. M.; Grupe, D. et al.
Partner: UNT Libraries Government Documents Department